Effective pulmonary capillary pressure.

The adult respiratory distress syndrome (ARDS) is almost invariably accompanied by permeability pulmonary oedema, usually appearing in the first few hours [1, 2]. The extent and therefore the seriousness of this oedema is proportional to the filtration of fluid and proteins through the pulmonary vascular endothelium. The extreme sensitivity of this filtration to variations of capillary pressure should lead us to consider any lowering, however small, of the latter as an essential treatment of permeability pulmonary oedema [3, 4]. Permeability pulmonary oedema (resuhing from an increase in pulmonary capillary permeability), contrasts with hydrostatic pulmonary oedema (resulting from an increase in hydrostatic pressure). The increase in capillary permeability is difficult LO observe; we are therefore led to define permeability pulmonary oedema as an oedema with no increase in hydrostatic pressure. Recemly, numerous experimental studies have questioned this dichotomy between hydrostatic and permeability pulmonary oedema. IL has been shown in sheep that, in the development of pulmonary oedema, an increase in hydrostatic pressure can be followed by an increase in permeability rsJ. Experimental studies on dogs have shown that a large increase in hydrostatic pressure can increase permeability [6]. Other studies have shown an increase in hydrostatic pressure and an increase in permeability to occur simultaneously [7]. Coincidence of an increase in hydrostatic pressure and an increase in pcrmeabiJiLy seems to be frequenL Does this coexis tence within the same experimental or clinical model question the necessity of distinguishing between them? I Lhlnk not.